The primary objective of this study was to determine whether there are changes in hypothalamic-pituitary-adrenal (HPA) axis activity associated with interruption of treatment with SSRIs, and if so, if the asociation is dependant upon drug half-life. The secondary objectives of this study are as follows: to collect comparative safeety data onmaintenance doses of fluoxetine, sertraline, or paroxetine by monitoring the reporting of spontaneous adverse events; to monitor the plasma concentrations of fluoxetine, sertraline, and paroxetine and their active metabolites following interruption of treatment, and to describe the relationship of the observed concentrations to discontinuation-emergent signs and symptoms (DESS) and stability of efficacy measures. The hypothesis tested was that HPA axis activation is a physiological marker of the dysphoric syndromes associated with short-acting SSRI withdrawal. To test this hypothesis, the investigators studied HPA axis function in patients treated with shorter-acting SSRIs as well as those in a control group treated with fluoxetine, a longer acting SSRI which does not appear to be associated with significant withdrawal symptoms.